1. Field of the Invention
This invention relates generally to single event upset (SEU) protection techniques, and more particularly to the protection and correction of state machine variables from SEUs.
2. Description of the Related Art
A single event upset (SEU) is a change in the state of a data bit that occurs due to ions or electromagnetic radiation striking a sensitive node in an electronic circuit; circuitry operating in space is particularly vulnerable to SEUs. A typical example is a storage element in a digital circuit, which might change state when exposed to radiation.
There are several engineering approaches to help ameliorate this problem. For example, circuitry can be designed using costly radiation-hardened processes. Another conventional approach to SEU protection is to use “triple-redundancy” and a voting circuit; this is illustrated in FIG. 1. Rather than use a single storage element to store a data bit, the bit is stored in three storage elements 10, 12, 14—here, D flip-flops connected to common data and clock lines. The Q outputs 16, 18, 20 of the flip-flops are provided to a voting circuit 22, which passes whichever data bit value is present on at least two of the three Q outputs on to an output 24. In this way, if one of the storage elements is “upset”, the other two storage elements out-vote it and hence the circuit still functions properly. However, this approach requires a considerable amount of logic and circuitry to function.